In inspection or examination for blood components in clinical tests, it is required to separate whole blood into serum or plasma (hereinafter occasionally referred to as “serum or the like”) and a component containing blood cells (hereinafter referred to as a “cell-containing component”). As one of the separation methods, there is known the method in which a whole blood sample is collected in a blood collection tube (hereinafter referred to merely as a “collection tube”) filled with a material having a specific gravity that is intermediate between those of the serum or the like and the cell-containing component, and the collection tube is subjected to centrifugal separation to place the material at a position between the serum or the like and the cell-containing component to thereby separate both the components from each other. According to the above method, the serum or plasma can be separated and collected using a pipette or by decantation without including blood cells in the serum or the like.
Hitherto, such a serum or plasma separating material is mainly formed of a gel-like material. For example, there has been proposed a serum separating material which contains an α-olefin-maleic acid diester copolymer having a specific viscosity as a main component and whose specific gravity is adjusted to the range of 1.035 to 1.055 (refer to Patent Document 1).
However, when separating the serum or plasma using such a soft gel-like separating material, the serum or the like thus separated in an inspection site tends to subsequently suffer from re-mixing with a cell-containing component owing to vibration upon handling a sample or erroneous absorption of the separating material therein upon dispensing, which will result in failure to obtain correct inspection results. In addition, the gel-like separating material tends to cause inclusion of electrolyte components contained in the blood cells into the serum or the like through an interface between an inner wall of the collection tube and the separating material or through a clearance formed inside of the separating material when stored for a long period of time or when preserved in a frozen state, which also leads to erroneous measurement results.
Also, there has been proposed a blood separating agent containing a polyether polyurethane having specific molecular weight, viscosity and density which is obtained by reacting a polyoxyalkylene glycol having a specific molecular weight with a diisocyanate as a main component, and an inert filler such as silica and alumina (refer to Patent Document 2). The blood separating agent used in Patent Document 2 has a specific gravity (density) which is overlapped with a specific gravity of the separating material of the present invention, and further a functional mechanism of the blood separating agent is similar to that of the present invention in such a point that the blood separating agent is transferred between a serum component and a cell-containing component by centrifugal separation procedure. In Patent Document 2, it is described that the separating agent is composed mainly of the polyether polyurethane as described above and forms a stable barrier upon completion of the centrifugal separation, and the barrier thus formed is not readily broken even when a container filled therewith is inclined or a weak impact is applied to the container, and is free from undesired change even when allowed to stand for a long period of time (column 3, lines 13 to 25 of Patent Document 2). However, even in the method described in Patent Document 2, there tends to still occur such a problem that after stored for a long period of time or preserved in a frozen state, a part of the cell-containing component is re-mixed in the serum component through an interface between an inner wall surface of the collection tube and the separating agent or through a clearance formed inside of the separating agent.
To solve the above conventional problems, there has been proposed the method in which after separating the serum or the like, the separating material is cured by irradiation with ultraviolet ray to completely separate respective components from each other (refer to Patent Documents 3 to 6).
However, it is considered that curing of the separating agent by irradiation with ultraviolet ray might give any adverse influence on measurement of components whose quality tends to be deteriorated by the ultraviolet ray irradiated (for example, bilirubin). In addition, it is usually required to sterilize a collection tube by irradiation with γ-ray, etc., so that the separating material disposed in the collection tube tends to be undesirably cured by the irradiation with γ ray, etc. Therefore, there tends to arise such a problem that the collection tube is incapable of being subjected to sterilization procedure.
On the other hand, in order to avoid undesirable change in quality of the respective components by irradiation with ultraviolet ray, there is known a method of curing the separating material by irradiating a reduced amount of ultraviolet ray thereto. However, since the respective blood components are present on both upper and lower sides of the separating material, the ultraviolet ray irradiated fails to reach a central portion of a resin of the separating material. Thus, it will be difficult to completely cure the resin inclusive of an inside portion thereof in the collection tube. As a result, there also tends to occur such a problem that the cell-containing component is re-mixed in the serum or the like, similarly to the above case where the uncured gel is used as the separating material.
Further, there has been proposed the method in which respective blood components are separated from each other using a porous three-dimensional fluid-transmissive bonded fiber structural body formed of specific polymeric fibers (refer to claims of Patent Document 7). In Patent Document 7, it is described that the structural body has a complicated inside network structure including a plurality of tortuous fluid flow paths through which particles entrained in the fluid are prevented from passing, and therefore serves as an excellent filtering device (refer to paragraph [0031] of Patent Document 7). In addition, Patent Document 7 discloses an elastomer multi-component (ECM) fiber as a specific material, and a thermoplastic elastomer as an example of the elastomer in the ECM fiber (refer to paragraphs [0050] and [0054] of Patent Document 7). However, in the method described in Patent Document 7, the material used therein fails to be transferred to a position between the serum component and the cell-containing component in view of a specific gravity thereof, and it is required that the material is previously disposed at the position by defining a boundary line between plasma and the solid blood component. Therefore, the method of Patent Document 7 needs a complicated procedure and has many problems since the method is not applicable as such to the existing inspection methods using a test tube.
Patent Document 1: Japanese Patent Publication No. S63-48310
Patent Document 2: Japanese Patent Publication No. H1-31588
Patent Document 3: U.S. Pat. No. 6,248,844
Patent Document 4: US. Patent Application Laid-Open No. 2007/187341
Patent Document 5: US. Patent Application Laid-Open No. 2008/108493
Patent Document 6: US. Patent Application Laid-Open No. 2008/132874
Patent Document 7: Published Japanese Translation of PCT Application No. 2008-538087